Later Hominins: The Australopithecine Gap

In April 2006, National Geographic ran a story titled “Fossil Find Is Missing Link in Human Evolution, Scientists Say,”⁵⁸ which reported the discovery of what the Associated Press called “the most complete chain of human evolution so far.”⁵⁹ The fossils, belonging to the species Australopithecus anamensis, were said to link Ardipithecus to its supposed australopithecine descendants.

What exactly was found? According to the technical paper reporting the find, the bold claims were based upon a few fragmented canine teeth which were said to be “intermediate” in size and shape. The technical description used in the paper was intermediate “masticatory robusticity.”⁶⁰ If a couple of four-million-year-old teeth of “intermediate” size and shape make “the most complete chain of human evolution so far,” then the evidence for human evolution must indeed be quite modest. Besides learning to distrust media hype, there is another important lesson to be gained from this episode. Accompanying the praise of this “missing link” were what might be called retroactive confessions of ignorance. In this common phenomenon, evolutionists acknowledge a severe gap in their evolutionary claims only after they think they have found evidence to plug that gap. Thus, the technical paper that reported these teeth admitted that, “Until recently, the origins of Australopithecus were obscured by a sparse fossil record,”⁶¹ further stating: “The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central problem in human evolutionary studies. Australopithecus species differ markedly from extant African apes and candidate ancestral hominids such as Ardipithecus, Orrorin and Sahelanthropus.”⁶² Following these comments, an article on MSNBC.com acknowledged that “Until now, what scientists had were snapshots of human evolution scattered around the world.”⁶³

Evolutionists who make retroactive confessions of ignorance risk the danger that the evidence that supposedly filled the gap may not turn out to be so compelling after all. This seems to be the case here, where a couple teeth of intermediate “masticatory robusticity” were apparently all that stood between an unsolved “central problem in human evolutionary studies,” and “the most complete chain of human evolution so far.”

Moreover, we’re left with the uncontested admission that the australopithecines “differ markedly” from their supposed ancestors — Ardipithecus, Orrorin, and Sahelanthropus. Given the fragmentary and enigmatic nature of those earlier species, a more objective analysis might lead to the suspicion that this period of supposed early hominin evolution remains what Tim White once called it: “a black hole in the fossil record.”⁶⁴

Australopithecines Are Like Apes

While Sahelanthropus, Orrorin, and Ardipithecus are controversial due to the fragmented nature of their remains, there are sufficient known specimens of the australopithecines to gain a better understanding of their morphology. Nonetheless, controversy remains over whether the australopithecines were upright-walking ancestors of the genus Homo.

Australopithecus, which literally means “southern ape,” is a group of extinct hominins that lived in Africa from a little over 4 mya until about 1 mya. “Splitters” (those paleoanthropologists who tend to see many different species in the fossil record) and “lumpers” (those who see fewer) have created a variety of taxonomic schemes for the australopithecines. However, the four most commonly accepted species are afarensis, africanus, robustus, and boisei. Robustus and boisei are larger boned and more “robust” than the others and are sometimes classified under the genus Paranthropus.⁶⁵ According to conventional evolutionary thinking, they represent a later-living offshoot that went extinct without leaving any living descendants today. The smaller “gracile” forms, africanus and afarensis (the species which includes the famous fossil “Lucy”), lived earlier, and are classified within the genus Australopithecus. These two latter species are commonly said to be directly ancestral to humans.

By far, the most well-known australopithecine fossil is Lucy. One of the most complete fossils among known pre-Homo hominins, she is commonly claimed to have been a bipedal ape-like creature which serves as an ideal precursor to the human species.

In 2009, Lucy’s skeleton came to the Pacific Science Center here in Seattle. Upon entering the room containing the thick glass case holding her bones, I was immediately struck by the incompleteness of her skeleton. Only 40% was found, and a significant percentage is mere rib fragments. Very little useful material from Lucy’s skull was recovered, yet she is one of the most significant specimens ever found.
There are some reasons for skepticism over whether the bones of “Lucy” represent a single individual, or even a single species. In a video playing at the exhibit, Lucy’s discoverer Donald Johanson admitted that when he found the fossil, the bones were scattered across a hillside, where he “looked up the slope and there were other bones sticking out.” Johanson’s written account explains further how the bones were not found together: “[S]ince the fossil wasn’t found in situ, it could have come from anywhere above. There’s no matrix on any of the bones we’ve found either. All you can do is make probability statements.”⁶⁶

This was therefore not a case where the bones were found connected, forming a contiguous skeleton. Rather they were scattered across a hillside. Ann Gibbons notes that Johanson’s “entire team fanned out over the gully to collect Lucy’s bones.”⁶⁷ At one point, Johanson explains that if there had been only one more rainstorm, Lucy’s bones might have been washed away, never to be seen again. This does not inspire confidence in the integrity of the skeleton: If the next rainstorm could have washed Lucy away completely, what might have happened during prior storms to mix her up with who-knows-what? Could “Lucy” represent bones from multiple individuals or even multiple species?

The classical rejoinder notes that none of Lucy’s bones appear duplicated, implying they come from a single individual. This is certainly possible, but given the fragmented and the incomplete and scattered nature of the skeleton, this rebuttal is far from conclusive. In particular, it’s difficult to say with high confidence that key portions of the skeleton — such as the half-pelvis and half-femur — are from the same individual. The pelvis and femur are, after all, her most studied bones, and are said to indicate she walked upright. As the Pacific Science Center exhibit boldly stated, “Lucy’s species walked bipedally, in much the same way as we do,” at one point claiming her skeleton “approximate[s] a chimpanzee-like head perched atop a human-like body.”

Lucy did have a small, chimp-like head in both size and shape. As University of Witwatersrand paleoanthropologist Lee Berger observes, “Lucy’s face would have been prognathic, jutting out almost to the same degree as a modern chimpanzee.”⁶⁸ But many have disagreed with claims that she looked like an ape-human hybrid. Bernard Wood refutes this misapprehension: “Australopithecines are often wrongly thought to have had a mosaic of modern human and modern ape features, or, worse, are regarded as a group of ‘failed’ humans. Australopithecines were neither of these.”⁶⁹

Moreover, many have challenged the claim that Lucy walked like we do, or was even significantly bipedal. Mark Collard and Leslie Aiello observe in Nature that much of the rest of her body was “quite ape-like,” especially with respect to the “relatively long and curved fingers, relatively long arms, and funnel-shaped chest.”⁷⁰ Their article also reports “good evidence” from Lucy’s hand-bones that her species “‘knuckle-walked,’ as chimps and gorillas do today.”⁷¹

Needless to say, paleoanthropologists who wish Lucy to be a bipedal precursor to our genus Homo disfavor the “knuckle-walking” interpretation. Collard and Aiello fall into this category, calling this evidence “counterintuitive,” and suggesting that “the locomotor repertoire of A. afarensis included forms of bipedalism, climbing and knuckle-walking.” This proposal is tenuous, however, since these forms of locomotion tend to be mutually exclusive. Nonetheless, they dismiss Lucy’s knuckle-walking specializations as “primitive retentions” from her ancestors.⁷² Science writer Jeremy Cherfas explains why this argument is doubtful:

Everything about her skeleton, from fingertips to toes, suggests that Lucy and her sisters retain several traits that would be very suitable for climbing in trees. Some of those same treeclimbing adaptations can still be detected, albeit much reduced, in much later hominids such as the 2-million-year old specimens of Homo habilis from the Olduvai gorge. It could be argued that Lucy’s arboreal adaptations are just a hangover from her treedwelling past, but animals do not often retain traits that they do not use, and to find those same features in specimens 2 million years later makes it most unlikely that they are remnants.⁷³

Apparently when the evidence points against Lucy being bipedal, it is simply discarded. But the main motivation for this dismissal is the evolutionary belief that modern humans need fully bipedal ape-like ancestors. Other leading paleoanthropologists also acknowledge that Lucy’s mode of locomotion was significantly different from that of humans. Richard Leakey and Roger Lewin argue that A. afarensis and other australopithecines “almost certainly were not adapted to a striding gait and running, as humans are.”⁷⁴ Their quotation of anthropologist Peter Schmid’s surprise at the non-human qualities of Lucy’s skeleton is striking:

“We were sent a cast of the Lucy skeleton, and I was asked to assemble it for display,” remembers Peter Schmid, a paleontologist at the Anthropological Institute in Zurich… “When I started to put [Lucy’s] skeleton together, I expected it to look human,” Schmid continues. “Everyone had talked about Lucy as being very modern, very human, so I was surprised by what I saw”… “What you see in Australopithecus is not what you’d want in an efficient bipedal running animal,” says Peter. “The shoulders were high, and, combined with the funnel-shaped chest, would have made arm swinging very improbable in the human sense. It wouldn’t have been able to lift its thorax for the kind of deep breathing that we do when we run. The abdomen was potbellied, and there was no waste, so that would have restricted the flexibility that’s essential to human running.”⁷⁵

Other studies confirm australopithecine differences with humans, and similarities with apes. Their inner ear canals — responsible for balance and related to locomotion — are different from those of Homo but similar to those of great apes.⁷⁷ Their ape-like developmental patterns⁷⁸ and ape-like ability for prehensile grasping by their toes⁷⁹ led one reviewer in Nature to say that whether australopithecines “were phylogenetically hominines or not, it seems to me that ecologically they may still be considered as apes.”⁸⁰ In 1975 C. E. Oxnard published a paper in Nature using multivariable statistical analysis to compare key australopithecine skeletal characteristics to living hominids. He found that australopithecines have “a mosaic of features unique to themselves and features bearing some resemblances to those of the orangutan” and concluded: “If these estimates are true, then the possibility that any of the australopithecines is a direct part of human ancestry recedes.”⁸¹ Even the teeth of Lucy’s species have been found to conflict with the hypothesis she was a human ancestor. A 2007 paper in Proceedings of the National Academy of Sciences (USA) reported “[g]orilla-like anatomy on Australopithecus afarensis mandibles,” which was “unexpected,” and “cast[s] doubt on the role of Au. afarensis as a modern human ancestor.”⁸²

As for Lucy’s pelvis, many have claimed it supports a bipedal form of locomotion, but Johanson and his team reported it was “badly crushed” with “distortion” and “cracking” when first discovered.⁸³ These problems led one commentator to propose in the Journal of Human Evolution that the reason Lucy’s pelvis is “so different from other australopithecines and so close to the human condition” was “error in the reconstruction… creating a very ‘human-like’ sacral plane.”⁸⁴ Another paper in the same journal concluded that the lack of clear fossil data about Lucy prevents paleoanthropologists from making firm conclusions about her mode of locomotion: “Prevailing views of Lucy’s posture are almost impossible to reconcile… To resolve such differences, more anatomical (fossil) evidence is needed. The available data at present are open to widely different interpretations.”⁸⁵

Paleoanthropologist Leslie Aiello, who served as head of the anthropology department at University College London, states that when it comes to locomotion, “[a]ustralopithecines are like apes, and the Homo group are like humans. Something major occurred when Homo evolved, and it wasn’t just in the brain.”⁸⁶

The “something major” that occurred was the abrupt appearance of the human body plan — without direct evolutionary precursors in the fossil record.

[Editor’s Note: This is an excerpt from Chapter 3, “Human Origins and the Fossil Record,” of the new book Science and Human Origins, co-authored by Ann Gauger, Douglas Axe, and Casey Luskin. For details, see Discovery Institute Press.]

References Cited

[58.] John Roach, “Fossil Find Is Missing Link in Human Evolution, Scientists Say,” National Geographic News (April 13, 2006), accessed March 4, 2012, http://news.nationalgeographic.com/news/2006/04/0413_060413_evolution.html.
[59.] Seth Borenstein, “Fossil discovery fills gap in human evolution,” MSNBC (April 12, 2006), accessed March 4, 2012, http://www.msnbc.msn.com/id/12286206/.
[60.] See Figure 4, Tim D. White, Giday WoldeGabriel, Berhane Asfaw, Stan Ambrose, Yonas Beyene, Raymond L. Bernor, Jean-Renaud Boisserie, Brian Currie, Henry Gilbert, Yohannes Haile-Selassie, William K. Hart, Leslea J. Hlusko, F. Clark Howell, Reiko T. Kono, Thomas Lehmann, Antoine Louchart, C. Owen Lovejoy, Paul R. Renne, Haruo Saegusa, Elisabeth S. Vrba, Hank Wesselman, and Gen Suwa, “Asa Issie, Aramis and the origin of Australopithecus,” Nature, 440 (April 13, 2006): 883-89.
[61.] Ibid.
[62.] Ibid.
[63.] Borenstein, “Fossil discovery fills gap in human evolution.”
[64.] Tim White, quoted in Gibbons, “In Search of the First Hominids,” 1214-19.
[65.] See for example Bernard A. Wood, “Evolution of the australopithecines,” in The Cambridge Encyclopedia of Human Evolution, eds. Steve Jones, Robert Martin, and David Pilbeam (Cambridge: Cambridge University Press, 1992), 231-40.
[66.] Tim White, quoted in Donald Johanson and James Shreeve, Lucy’s Child: The Discovery of a Human Ancestor (New York: Early Man Publishing, 1989), 163.
[67.] Gibbons, The First Human: The Race to Discover our Earliest Ancestors, 86.
[68.] Berger and Hilton-Barber, In the Footsteps of Eve: The Mystery of Human Origins, 114.
[69.] See for example Bernard A. Wood, “Evolution of the australopithecines,” 232.
[70.] Mark Collard and Leslie C. Aiello, “From forelimbs to two legs,” Nature, 404 (March 23, 2000): 339-40.
[71.] Collard and Aiello, “From forelimbs to two legs,” 339-40. See also Brian G. Richmond and David S. Strait, “Evidence that humans evolved from a knuckle-walking ancestor,” Nature, 404 (March 23, 2000): 382-85.
[72.] Ibid.
[73.] Jeremy Cherfas, “Trees have made man upright,” New Scientist, 97 (January 20, 1983): 172-77.
[74.] Richard Leakey and Roger Lewin, Origins Reconsidered: In Search of What Makes Us Human, (New York: Anchor Books, 1993), 195.
[75.] Ibid., 193-94.
…
[77.] Fred Spoor, Bernard Wood, and Frans Zonneveld, “Implications of early hominid labyrinthine morphology for evolution of human bipedal locomotion,” Nature, 369 (June 23, 1994): 645-48.
[78.] See Timothy G. Bromage and M. Christopher Dean, “Re-evaluation of the age at death of immature fossil hominids,” Nature, 317 (October 10, 1985): 525-27.
[79.] See Ronald J. Clarke and Phillip V. Tobias, “Sterkfontein Member 2 Foot Bones of the Oldest South African Hominid,” Science, 269 (July 28, 1995): 521-24.
[80.] Peter Andrews, “Ecological Apes and Ancestors,” Nature, 376 (August 17, 1995): 555-56.
[81.] Oxnard, “The place of the australopithecines in human evolution: grounds for doubt?,” 389-95.
[82.] Yoel Rak, Avishag Ginzburg, and Eli Geffen, “Gorilla-like anatomy on Australopithecus afarensis mandibles suggests Au. afarensis link to robust australopiths,” Proceedings of the National Academy of Sciences (USA), 104 (April 17, 2007): 6568-72.
[83.] Donald C. Johanson, C. Owen Lovejoy, William H. Kimbel, Tim D. White, Steven C. Ward, Michael E. Bush, Bruce M. Latimer, and Yves Coppens, “Morphology of the Pliocene Partial Hominid Skeleton (A.L. 288-1). From the Hadar Formation, Ethiopia,” American Journal of Physical Anthropology, 57 (1982): 403-51.
[84.] François Marchal, “A New Morphometric Analysis of the Hominid Pelvic Bone,” Journal of Human Evolution, 38 (March, 2000): 347-65.
[85.] M. Maurice Abitbol, “Lateral view of Australopithecus afarensis: primitive aspects of bipedal positional behavior in the earliest hominids,” Journal of Human Evolution, 28 (March, 1995): 211-29 (internal citations removed).
[86.] Leslie Aiello quoted in Leakey and Lewin, Origins Reconsidered: In Search of What Makes Us Human, 196. See also Bernard Wood and Mark Collard, “The Human Genus,” Science, 284 (April 2, 1999): 65-71.